Geologist Trevor Williams, of Columbia University's Lamont-Doherty Earth Observatory, will be spending six weeks at Antarctica's McMurdo Station, taking part in a study of the sea-floor sediments beneath the Ross Ice Shelf. The results could aid our understanding of climate change. Williams will be filing reports here throughout the project. Listen to him live from the bottom of the Earth here.

ROSS ISLAND, Antarctica, Dec. 14 — The Earth is bi-polar. The North Pole and South Pole each have their own distinct personalities. The North Pole is covered by a few feet of floating sea ice, while the South Pole sits on a 9000-feet-thick continental ice sheet. So the North Pole is much more vulnerable to losing its ice than the South Pole.

Research published this week predicts that the Arctic could become nearly free of ice during summertime as early as 2040. The research team of Marika Holland, Cecilia Bitz and Bruno Tremblay ran computer simulations of Arctic climate, oceanography and sea ice, and found that the Arctic is likely to experience abrupt losses of summer ice cover in the coming decades.

First, they tested the computer model—based at the National Center for Atmospheric Research—against known changes in ice cover since 1870. This test matched the observations well, so the team proceeded to simulate future ice loss, assuming greenhouse gases in the atmosphere continue to build up. All of their seven simulations predict periods of steady ice loss at a similar rate to today, followed by periods of rapid retreat, when over 7% of the current ice area will be lost each year. By 2050, all the simulations have September ice cover at less than 10% of the current area. The Arctic will still ice over in winter, but it will be thinner than today.

The Arctic melting is faster than previously had been predicted—probably because the computer model is now more realistic, and includes feedbacks: Open water absorbs sunlight better than ice, so the more open water there is, the faster the ice melts. Plus, in this model, warm ocean currents from the Atlantic push further north into the Arctic.

While the loss of ice is good news for new shipping routes and fishing grounds, it is bad news for people who rely on the sea ice for their living—and bad news for the symbol of the Arctic, the polar bear. Perhaps most alarmingly, the faster Arctic warming will accelerate the melting of the permafrost in northern Canada and Siberia, releasing methane, a potent greenhouse gas.

Holland's research is part of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment. The IPCC assessment is a big deal—a comprehensive overview covering state-of-the-art knowledge about climate change. When released in February, it is sure to generate a lot of coverage and debate, and, perhaps, prompt some government action.

Can we apply similar computer simulations to predict when the Ross Ice Shelf (my home for two months) might break up in a warmer world? It's not easy. The ice sheet does not break up by thinning and melting like the Arctic ice, but by iceberg calving. We know icebergs will break off, but, like earthquakes, it is very difficult to predict exactly where or when this will happen. For example, in 2002, the break-up of the Larsen B ice shelf (about the size of Rhode Island) from the Antarctic Peninsula came as a big surprise to scientists.

Instead of computer modeling, ANDRILL's approach down here is to discover how the Ross Ice Shelf responded to natural climate changes of the geological past. If we know the ice sheet rarely survived a certain temperature in the past, we will know that this will also be a critical temperature in the future.

On a lighter note, I'm happy to say that this week I met my first Antarctic penguins—walking about, waving their flippers and full of personality. It's a real treat to see them in their natural habitat. But has it always been so? Take a look at the cave painting at right; it dates from 18,500 years ago, at the height of the last glacial advance, when penguins enjoyed the cold climates in, of all places, the south of France. I love the idea that penguins once journeyed so far from their present home. –Trevor Williams

EARLIER FROM ANTARCTICA: The Science of Ice (Log #3), First Days on the Ice (Log #2), Journey to the Bottom of the Earth (Log #1)